Presentation at the 2008 MGP Conference

1. A Multi-Technique Approach for an Evaluation of the Effectiveness of a Creosote Containment System at a Former New England Wood Treating Facility by T. Jordan, N. Misquitta, M. Brourman, and M Bollinger

2. Background Information Former Wood Treating Facility Operated from 1923 – 1982. Sandy fluvial deposits overlying glacial till and meta-sedimentary bedrock.

3. Facility Operations - 1931

4. Wood Treatment Operations

5. Site Conditions - 1997

6. Site Conditions - 2005

7. Remedies Sheetpile Barrier Wall System - 1997 NAPL Recovery Wells and Sumps Installed 1997 – 2002. Transition from onsite groundwater treatment and discharge to POTW to onsite groundwater recirculation and NAPL recovery. Infiltration Gallery Constructed

8. Site Setting

9. Site Setting Source Area – Closed Impoundment

10. Groundwater Flow Directions Infiltration Gallery

11. Locations of Product Recovery Sumps and Wells

12. Extent of NAPL Mapped by Others

13. Profile of Sheetpile Barrier Wall and Vicinity

14. Sheetpile Barrier Wall

15. Sheetpile Barrier Wall – As-Built Area Where NAPL on River Sediments Have Been Noted

16. Objectives of This Study Determine if NAPL Going Under the SBS. Determine if NAPL Going Through the SBS. Determine the lateral and vertical extent of NAPL. Determine if NAPL is laterally Circumventing the Extent of the SBS.

17. Approach Perform Critical Gradient Analysis using existing data to assess NAPL mobility at SBS (Cohen & Mercer, 1993). Perform dye tests to evaluate SBS. Collect TarGOST® and CPT data to address data gaps. Complete additional test borings to ground-truth TarGOST® information. Construct 3-D Conceptual Site Model to interpret data.

18. Critical Gradient Analysis Use a flownet to calculate the vertical gradient component near the SBS. Use site specific physical properties of NAPL to determine mobility (Cohen & Mercer, 1993).

19. NAPL Properties

20. Site Topography

21. Is NAPL Going Under the SBS When River Level is High?

22. Is NAPL Going Under the SBS When River Level is Low?

23. SBS Versus TarGOST® Borings

24. Results of Critical Gradient Analysis River stage controls vertical gradient components in the vicinity of the SBS. Highest vertical gradient components at low river levels. Highest vertical gradient components are anticipated near the SBS and decrease away. Low river stage results in sufficient upward gradients to mobilize NAPL in river sediments. 3-D model of as-built drawings and new test borings indicate that the SBS may not be completed deep enough in the area of concern.

25. Is NAPL Going Through the SBS?

26. Dye Test Well Clusters

27. TarGOST® and CPT Methods

28. TarGOST® Borings

29. Geology from CPT and Plume Extent from TarGOST®

30. TarGOST® and CPT Results Alternating thin layers (2 – 4 cm thick) of silty sand and sandy silt. Thin seams of free NAPL present in more permeable thin layers. Two zones of free NAPL identified: Immediately below the water table <1 to >4 meters above the top of the glacial till

31. Lateral Extent of NAPL SBS

32. Results Critical gradients during low river stage are sufficient to mobilize residual NAPL in river sediments. Therefore, NAPL occurrences in the vicinity of the SBS may not be indicative of NAPL moving through the wall. Extent of NAPL has been characterized in 3-D. NAPL appears to be circumventing the ends of the SBS. NAPL may possibly be migrating beneath the SBS in areas where the contractor was unable to drive sheets to sufficient depth.

33. Approach for Remediation